Volumetric displays are a class of three-dimensional display technology that produce volume-filling imagery. Typically, volumetric displays are autostereoscopic; that is, they produce imagery that appears three-dimensional without the use of additional eyewear.
Some volumetric displays create three-dimensional imagery by employing spatio-temporal multiplexing in emitting or scattering light from a range of locations within an image volume. In other words, a smaller number of light-generating devices (for example, lasers, projector pixels, etc.) are run at a higher frequency than an overall volumetric refresh rate, and the light is imaged onto a rotating surface. Persistence of vision integrates the image slices formed at different spatio-temporal locations of the volume swept by the rotating surface, and the viewer perceives a volume-filling, three-dimensional image.
The concept of a volumetric display in which three-dimensional imagery is perceived by visual integration of a series of images projected on a rotating screen has existed since, at least, the late 1950s. In 1958, Max Hirsch filed a patent application for a “generescope,” wherein imagery formed on the surface of a cathode ray tube (CRT) is relayed by a periscope-like arrangement that images onto a rear-projection screen. In the generescope, the CRT, mirrors, and screen rotated in unison. The arrangement of rotating relay mirrors keeps the projection optical path length invariant with respect to the projection screen angle. For this, Hirsch was issued U.S. Pat. No. 2,967,905 in 1961.
A 1960 Aviation Week article entitled “New Display Gives Realistic 3-D Effect,” (pp. 66-67, Oct. 31, 1960) describes a 3-D display developed by ITT Laboratories. It is similar to the display taught by Hirsch, in that a sequence of 2-D images formed on the surface of a CRT are relayed to a rotating projection screen by an arrangement of mirrors that rotate with the projection screen, thereby keeping the projection optical path length invariant with respect to the projection screen angle. However, the ITT display employs a stationary CRT and front-end optical components. One consequence of their architecture is that the CRT's image rotates in the plane of the projection screen as the projection screen rotates.
Other volumetric displays which employ similar radially-extended relay optics include the volumetric displays described by Batchko (U.S. Pat. No. 5,148,310) and Tsao et al. (U.S. Pat. Nos. 5,754,147 and 5,954,414). Batchko describes a volumetric display wherein a rotating screen is illuminated by a fixed, vector-scanned laser illumination source. Tsao and co-workers utilize a k-mirror system, which rotates at half of the screen's angular frequency, to prevent the image of the projector from rotating in the plane of the projection screen.